The present invention relates to the sterilization and disinfection arts. It finds particular application in conjunction with electrochemically produced solutions containing oxidizing agents, such as peracetic acid, for sterilization or disinfection of medical and pharmaceutical equipment, food products, and the like, and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to other sterilization, disinfection, and sanitization methods, including treatment of water, food service equipment, and the like and has applications in bleaching and in chemical synthesis.
Peracetic acid is a useful disinfectant or sterilant for a variety of applications. Peracetic acid has a number of uses, including disinfection of waste and sterilization of medical equipment, packaging containers, food processing equipment, and the like. It poses few disposal problems because it decomposes to compounds (i.e., acetic acid and oxygen) which are readily degraded in sewage treatment plants or by soil bacteria. It has a broad spectrum of activity against microorganisms, and is effective even at low temperatures.
Conventionally, peracetic acid concentrations are produced from solutions of acetic acid and hydrogen peroxide at acidic pH. The concentrated solutions are mixed with water and other chemicals to form a dilute solution. Items to be decontaminated, either by sterilization or disinfection, are then immersed in the solution for a sufficient period to effect the required level of decontamination. The decontaminated items are then typically rinsed before use. To ensure effective sterilization or disinfection within a preselected period of time, the concentration of peracetic acid is preferably at or above a minimum effective level, typically around 1000-2000 ppm for sterilization of medical instruments. When the peracetic acid concentration is at or above the minimum effective level for sterilization, sterilization is expected in the time period for contact. Lower levels of peracetic acid are effective as disinfectants. Concentrations as low as 2-10 ppm, or less, have been shown to be effective for disinfection, which requires only the destruction of pathogenic microorganisms.
While single use formulations of peracetic acid are available, in facilities where items are being sterilized or disinfected at frequent intervals throughout the day, the same batch of peracetic acid solution is often used repeatedly. However, peracetic acid tends to decompose over time. For example, a disinfectant solution, which is above the minimum effective peracetic acid concentration for sterilization at the beginning of a day, frequently drops below the effective concentration without further additions of the concentrated peracetic acid or precursors. Elevated ambient temperatures, the quantity of items sterilized or disinfected, and the degree of contamination of the items, all contribute to reducing the useful life of the batch. In addition, storage conditions sometimes lead to degradation of the peracetic acid precursors before use.
Moreover, the concentrated peracetic acid or precursors tend to be hazardous materials which sometimes pose shipment and storage problems. Because of the risks of storage and also the fact that they degrade over time, it is preferable to maintain a limited supply of the concentrate or precursors and reorder them at frequent intervals.
Recently, the cleaning and decontamination properties of solutions formed by the electrolysis of water under special conditions have been explored. Electrolysis devices are known which receive a supply of water, such as tap water, commonly doped with a salt, and perform electrolysis on the water. During electrolysis, an anolyte solution is produced from the doped water at an anode and a catholyte solution is produced at a cathode. Examples of such water electrolysis units are as described in U.S. Pat. Nos. 5,635,040; 5,628,888; 5,427,667; 5,334,383; 5,507,932; 5,560,816; and 5,622,848.
To create these anolyte and catholyte solutions, tap water, often with an added electrically or ionically conducting agent, is passed through an electrolysis unit or module. The unit has an anodic chamber and a cathodic chamber, generally separated from each other by a partially-permeable barrier. Conducting agents are often halogen salts, including the salts sodium chloride and potassium chloride. An anode and a cathode contact the water flowing in the respective anodic and cathodic chambers. The anode and cathode are connected to a source of electrical potential to expose the water to an electrical field. The barrier may allow the transfer of selected electron carrying species between the anode and the cathode but limits fluid movement between the anodic and cathodic chambers. The salt and minerals naturally present in and/or added to the water undergo oxidation in the anodic chamber and reduction in the cathodic chamber.
An anolyte resulting at the anode and a catholyte resulting at the cathode can be withdrawn from the electrolysis unit. The anolyte and catholyte may be used individually or as a combination. The anolyte has been found to have anti-microbial properties, including anti-viral properties. The catholyte has been found to have cleaning properties.
However, electrochemically activated water is not without shortcomings. Electrochemically activated water has a high surface energy, which does not readily allow for penetration of the electrochemically activated water into creviced areas of medical instruments. Thus, complete kill may not be achieved. Further problems have arisen on metal surfaces coming into contact with the electrochemically activated water, including the surfaces of the decontamination equipment and metal medical devices. The electrochemically activated water is corrosive to certain metals. Stainless steel, used to produce many medical devices, is particularly susceptible to corrosion by electrochemically activated water.
Other chemicals are also amenable to electrochemical conversion. Khomutov, et al. (xe2x80x9cStudy of the Kinetics of Anodic Processes in Potassium Acetate,xe2x80x9d Izv. Vyssh. Uchebn. Zaved., Khim. Teknol. 31(11) pp. 71-74 (1988)) discloses a study of the conversion of acetate solutions to peracetic acid and acetyl peroxide in the temperature range of xe2x88x9210xc2x0 C. to 20xc2x0 C. using a three-electrode cell. The anode and cathode regions of the cell were separated by a barrier of porous glass. Anodes of platinum, gold or carbon, at a high potential, typically 2-3.2 V relative to a silver/silver chloride reference electrode, were used in the study. Potassium acetate concentrations were initially 2-10 mol/L. From conductivity and viscosity measurements, Khomutov, et al. estimated that peracetic acid solutions were generated at the anode with concentrations of active oxygen of 0.1 gram equivalents/L. However, no direct measurements of peracetic acid concentration in the bulk solution were made. Moreover, the pH range of 8.2-10.4 disclosed by Khomutov, et al. is undesirable for many practical decontamination solutions. To reduce corrosion of the metal components of the instruments to be decontaminated, a pH of close to neutral is desirable.
The present invention provides a new and improved system and method for generation of peracetic acid and other oxidizing agents which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method for preparing an antimicrobial solution containing peracetic acid is provided. The method includes electrolytically generating hydrogen peroxide or peroxide ions or radicals and reacting such species with an acetyl donor to form peracetic acid.
In accordance with another aspect of the present invention, a method of antimicrobial decontamination of items is provided. The method includes supplying an oxygen containing gas to a cathode of an electrolysis unit and forming peroxide species, such as peroxide ions, peroxide radicals, or hydrogen peroxide, in an electrolyte at the cathode. The method further includes reacting the peroxide species with a peracetic acid precursor to form peracetic acid and transporting the electrolyte containing peracetic acid to a site at which the items are microbially decontaminated.
In accordance with another aspect of the present invention, a system for antimicrobial decontamination of items is provided. The system includes an electrolysis unit including an anode and a cathode. A source of an electrical potential applies a potential between the anode and the cathode. A source of an oxygen containing gas supplies oxygen to the cathode for forming peroxide species in an electrolyte. A source of a peracetic acid precursor supplies a peracetic acid precursor for reacting with the peroxide species to form a solution which includes peracetic acid. A vessel receives items to be decontaminated and a fluid supply line carries the solution containing peracetic acid from the electrolysis unit to the vessel.
One advantage of the present invention is that it enables peracetic acid solutions to be prepared in situ, as required, or stored in small batches, until needed.
Another advantage of the present invention is that it enables antimicrobial solutions to be provided on line or in batch form, on demand.
Yet another advantage of the present invention is that the peracetic acid concentration of a solution can be revived or increased by returning the solution to an electrolysis unit.
A further advantage of the present invention is that storage and shipment of concentrated and hazardous sterilants or precursors may be avoided.
A yet further advantage of the present invention arising from the generation of peracetic acid on demand is that decomposition of peracetic acid during shipment and storage is avoided.
Another advantage of the present invention is that it enables the concentration of peracetic acid in a microbial decontamination system to be maintained during repeated use of the system.
Yet another advantage of the present invention is that concentrations of peracetic acid in the range of about 1000 to 2000 ppm can be prepared for sterilization or other applications without employing high concentrations of precursors.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.